Age, body weight, and pregnancy loss

Abstract

T he causes of embryo loss (< 40 days) are both known and speculative.1 Ball (1988) 2 reviewed reported research up to that time. Persistent mating-induced endometritis may be a cause of both lowered conception rate and embryo loss due to bacterial infection or persistence of inflammatory fluids.3,4 An association between multiple pregnancy and embryo size for age with embryo loss has been recently reported.5 There is, however, a percentage of “normal” single pregnancies in healthy young mares which fail for no apparent reason. Studies in other species suggest that levels of nutrition at halfor double-maintenance have adverse effects on embryo survival.6 Observations by breeders and stud managers have suggested that mares, although cyclic, have reduced conception rates when experiencing weight loss and that significant weight loss in early pregnancy is associated with embryo loss. Previous analysis of data from the farm in this study showed that mares losing more than 50 kg were highly likely to lose their pregnancy (unpublished). Various studies have shown the effects of nutrition levels on reproductive function. Guillaume and others (2002)7 restricted diets of ponies over 18 months. The onset of anoestrus was advanced, and the effect of photostimulation was inhibited. Godol and others (2002)8 showed that increasing body condition reduced the parturition to ovulation and the inter-ovulatory intervals. Banach and Evans (1981),9 however, found no adverse effect of a diet restricted in the last 90 days of pregnancy. Mitchell and Allen (1975)10 attributed a 46% embryo loss in yearlings to the effect of nutritional and other stress factors. Van Niekerk (1965)11 also found that se-